antidiffusion

Antidiffusion is a conceptual opposite to diffusion, a process where particles spread out from an area of high concentration to an area of low concentration. Instead of dispersion, antidiffusion describes a phenomenon where particles move from a region of low concentration towards a region of high concentration, effectively concentrating themselves. This process is not a spontaneous, natural occurrence in typical physical systems governed by the second law of thermodynamics, which favors increasing entropy and thus spreading out.

However, antidiffusion can be observed or induced in specific contexts. For instance, in some complex fluid dynamics or plasma physics scenarios, external forces or carefully engineered conditions can create situations that mimic antidiffusion. These can involve non-equilibrium states or the presence of specific types of interactions between particles. In computational modeling, antidiffusion terms are sometimes added to diffusion equations to counteract numerical diffusion, which is an artifact of discretization that artificially spreads out sharp features in a solution. This is done to preserve the integrity of the simulation rather than representing a physical process. Theoretical explorations also consider antidiffusion in abstract mathematical frameworks, sometimes as a tool for understanding the behavior of systems under non-standard conditions.